Load indicating device for compacting press



June 25, 1968 GR|E$HE|MER ET AL 3,389,432

LOAD INDICATING DEVICE FOR COMPACTING PRESS 4 Sheets-Sheet 5 Filed April 18, 1966 Fig. 6

INVENTORS flay/1205 sum/mm mm) L 0mm, J2

BY ,ym. 124;,

ATTORN EYS June 25, 1968 GR|E$HE|MER ET AL 3,389,432

LOAD INDICATING DEVICE FOR COMPACTING PRESS 4 Sheets-Sheet 4 Filed April 18, 1966 wmw wfik United States Patent 3,389,432 LOAD INDICATING DEVICE FOR C(lMPACTlNG PRESS Richard E. Griesheimer, Cincinnati, and Richard L.

Cahail, Jr., Batavia, Ohio, assignors to The Cincinnati Shaper Company, Cincinnati, Ohio, a corporation of Ohio Filed Apr. 13, 1966, Ser. No. 543,186 Claims. (Cl. 18--16.7)

This invention relates to a load indicating device for a compacting press. Actually the purpose of the load indicator is to indicate the density of the compacted piece and to provide for load release, sorting of products beyond the allowable density range and the like.

While the invention is capable of many uses, it is particularly adapted for use with a compacting press of the multiple platen type such as is described in detail in the Belden patent, No. 3,172,156, dated Mar. 9, 1965. In such a press, there is provided a ram and a number of floating platens each of which carries a die and a fixed platen. There may also be a core load it the article to be compacted is to be hollow or have a counterbore.

In such a press, it will be understood that the main ram applies the total load and that the total load applied by the main ram may be distributed among the several platens and perhaps the core rod if one is used. The load, of course, is not shared equally by the various platens but in order to achieve a uniform density, the load should be shared in amounts which are proportional to the relative areas of the compacted material which are supported by the respective dies and/or the core rod.

It is of great importance in the making of workpieces from powdered metal by compacting, that the density be uniform throughout the workpiece. If the density is nonuniform, zones of weakness are created and the piece is liable to fracture.

In general, the density of each level of compacted part is directly proportional to the load per unit area under compression so long as the type of powder, the powder additives, powder size, mixture content, and the like, are held constant. From this it can be seen that if the powder parameters are maintained constant, a load indicating means which will separate out and give readings of loads on any given part level will give a measure of the density.

With the foregoing considerations in mind, it is an object of the present invention to provide means for measuring the density by measuring the load carried by each of the elements in the compacting press. It is another object of the invention to provide electrical means for amplifying the readings and indicating them, as well as to provide switching means whereby the different part levels may be measured individually, as well as means for balancing the system. Further objects of the invention include the provision of means for setting allowable ranges for maximum and minimum density, and the provision of an overload release which will stop the press in the event an overload is registered.

These and other objects of the invention which will be described in more detail hereinafter, or which will be apparent to one skilled in the art upon reading these specifications, are accomplished by that certain construction and arrangement of parts of which the following describes an exemplary embodiment.

Reference is made to the drawings forming a part hereof and in which:

FIG. 1 is a somewhat diagrammatic view of a compacting press according to the Belden patent mentioned above, with parts in section to show how the various pressures are measured.

FIG. 2 is a bottom plan view of a transducer element with parts in section to show the mounting of the strain gauges.

FIG. 3 is a cross sectional view of the same taken on the line 3-3 of FIG. 2.

FIG. 4 is a plan view on a greatly enlarged scale of a typical strain gauge.

FIG. 5 is a block diagram showing the operation of the device.

FIG. 6 is a fragmentary cross sectional view of the main ram showing how the ram transducer is secured to the ram and the punch adapted is secured to the transducer.

FIG. 7 is a diagrammatic plan view of a gating device; and

FIG. 8 is a front elevational view of the same.

Basically, the pressure or load carried by any element of the press is measured by measuring the deformation of an element subjected to the load. Thus, the main ram, standard platen, lower platen, stationary punch, and also the core rod, if one be used, each carries a transducer, which is basically a collar; and during the operation of the press, this collar will be subjected to compression. Conventional strain gauges are mounted on each of the transducers in pairs, and the pairs of strain gauges are connected across a Wheatstone bridge arrangement. During the operation of the press, the bridges will be unbalanced and thus give a very minute electrical signal; and this signal is amplified and fed through a peak motion indicator to a meter which may be calibrated in tons. The peak motion indicator is simply to receive an extremely rapid signal and supply a corresponding signal to the meter in a quasi-static manner that may be read, since the action of the press is extremely rapid and the needle of the meter would simply bounce back and forth, and would not remain still long enough for a reading.

A density control circuit is provided which has settings for high and low limits and is provided with high and low limit relays. These relays may be caused to produce a visual or audible signal or to operate a shunting mechanism to guide the defective pieces into a different path or paths than the pieces having a density within the allowable range.

Coming now to a more detailed description, the trans ducer is shown in FIGS. 2 and 3 in some detail. It is indicated generally at 10 and is in effect a collar having the flanges 11 and 12 and the reduced thickness annular section 13. Secured to the wall 13 are two pairs of strain gauges 14 and 15. These strain gauges are extremely minute and one is shown in a very greatly enlarged view in FIG. 4. Each one is provided with the soldering terminals 16 and the grid 17 of very fine resistance wire or foil. These strain gauges are adhesively secured to the wall 13 with the gauges 14 being disposed horizontally, and the gauges 15 being disposed vertically as shown in FIG. 4. These strain gauges are actually resistors having a resistance, in the particular instance being described, of 350 ohms. It will be understood that the resistors which are vertically mounted will be compressed when the transducer is subjected to ram pressure and thus the wires of the grid 17 being compressed will be thickened slightly, and the resistance will be reduced.

On the other hand, the strain gauges 14 which are horizontally mounted will be stretched when the transducer 10 is under compression, because compression of the wall 13 will cause a very slight increase in its circumference. As is well understood, the pairs. of strain gauges 14 and 15 will be connected in opposition in a Wheatstone bridge arrangement, and an energizing voltage of, say, 15 volts DC, will be supplied across opposed corners of the bridge. Thus, when the transducer is subjected to compression, the bridge will be unbalanced, and leads extending from the two intermediate corners of the bridge will show a very minute voltage (in the millivolt range). This small voltage of course will be proportional to the unbalancing of the bridge, and this in turn is proportional to the compression on the transducer.

As can be seen from FIG. 1, the die platen D carries no load, and therefore is not provided with a transducer. The transducer is associated with the main ram R and will give an indication of the total load on the press. A transducer 10a, also provided with strain gauges as above described, is arranged to take the load of the standard platen 18. Another transducer 10b is arranged to indicate the load taken by the lower platen 19. A transducer 160 is arranged to indicate the load on the stationary punch and a transducer 10a is arranged to indicate the load on the core rod if one is used (none is shown in FIG. 1).

It will be understood that for accurate readings it is desirable that the transducers themselves not be subjected to any preload. It is also desirable that the transducers themselves be preassembled with the strain gauges and completely wired, and be capable of easy replacement by the machinist without the need of special training or special tools. Thus one flange, i.e. the flange 11 of FIG. 1, is provided with three holes 21 which are counterbored at 22 for bolt heads. The transducer 10 is secured to the ram as shown in FIG. 6 by means of three bolts 23 passing through the holes 21 and into the ram R. The flange 12 carries three large bores aligned with the holes 21 and indicated at 24 for access to the heads of the bolts 23 by means of an Allen wrench or the like. Thus, there will be three holes 24. Equally spaced intermediate the holes 24 in the flange 12 are the tapped holes 25; and bolts 26 passing through the holes in the flange of adapter A secure the adapter A to the transducer 10 (FIG. 6). From this description, it will be clear that the only stress to which the transducer 10 is subjected is the weight of the adapter and the punch P which is held thereby. This stress is negligible in comparison with the load of the press under operating conditions.

It will also be understood that the four strain gauges 14, 15 are properly wired in a Wheatstone bridge arrangement with the four leads from the bridge connected into a plug 14-15 adapted to be plugged into a mating socket. The leads pass out through the channel 12a in the flange 12, and a mating channel in the flange of the adapter A. Thus, if it is necessary to replace a strain gauge or the entire transducer, it is only necessary to remove the adapter by removing the bolts 25 and insert an Allen wrench through the holes 24 in the transducer and unscrew the bolts 23. The transducer is then removed from the ram. The plug can then be removed from the socket and the entire transducer replaced by bolting a new transducer to the ram, bolting the adapter to the transducer, and plugging in the electrical connections.

The transducers on the several platens and stationary punch and core rod are of course secured in position and plugged in in the same manner as described above in connection with the main ram.

In FIG. 5 there is shown a block diagram of the apparatus showing the relationship of the various parts to each other. The block diagram has been used because it is believed to contribute to a full understanding of the invention and the Wiring diagram is within the skill of a competent electrical engineer.

From the block diagram, it will be seen that by means of the switch element 30 a connection may be made to any of the transducers. In this particular block diagram, four transducers are shown, there being one for the ram, one for each of the two floating platens, and one for the fixed platen or stationary punch. It will be understood that if more floating platens are provided or if a core punch is provided there will be additional transducers. The signal from the selected transducer may then be selectively passed on to the automatic balance and the transducer amplifier for low scale or high scale operation by positioning the switch element 31. This simply involves an electrical multiplier which in itself does not constitute a part of the present invention.

It will be noted that a calibration bridge has been provided and that the switch element 31 may be moved to three positions in connection with the calibration bridge. In the zero position of the switch element 31, the calibration bridge is connected to automatic balance and transducer amplifier. The automatic balance zeroes the amplifier automatically with respect to the calibration bridge. By moving the switch element 31 to the Cal. meter position, the meter 32 is calibrated and by moving the switch element 31 to the Cal. limits position, the high and low limit elements of the density control circuit may be set.

The elements enclosed within the block 33 constitute the density control circuit and those within the block 34 in conjunction with those within block 33 constitute the automatic balancing circuit. The element 34 is a commerically available device known as Automatic Tare, available from Automatic Timing and Controls, King of Prussia, Pa. Similarly, the density control circuit within the block 33 is available on the open market as a relay operator with high and low limit operation, also from Automatic Timing and Controls of King of Prussia, Pa.

As before indicated, the power supply for the transducers is 15 volts DC. and assuming that the circuits have all been calibrated and balanced, the switch element 30 is positioned for the particular transducer it is desired to read. The switch element 31 is positioned for either low scale or high scale operation. The very weak signal (in the millivolt range) from the particular transducer is fed into the automatic balancing circuit and the output is then amplified by the transducer D.C. amplifier so that the output voltage has a range of zero to 6 volts DC. and it is this signal which is ultimately impressed upon the meter 32 which is calibrated in tons. Because the signal from the transducer will be a very momentary one because of the extremely rapid application of pressure, it would be impossible to obtain a visual reading from the meter 32 and for this reason the signal passes first through a peak motion indicator. This is also a conventional device available on the open market and it operates by capacitors which are charged by the momentary surge and then discharged gradually so that the needle of the meter 32 will hold a reading for several seconds before decaying.

High and low limits can be set in the density control device 33 and if the range set into the circuit is exceeded in either direction, the appropriate high or low limit relay will function. The relay may be caused to operate any desired sort of signaling device as colored lights, alarm bells, or the like, or they may actuate a gating device so that workpieces which have a density within the preset limits move along one path, whereas if the maximum density is exceeded the high limit relay may actuate a gate to shunt dense workpieces into a different path and if the minimum density is not achieved, the low limit relay may operate a gate to shunt the low density workpieces into another path.

The box 35 represents the overload device and comprises an overload detector and an overload relay. These elements are substantially the same as those in the density control circuit. The relay may be arranged to actuate a switch to shut the press off in the event of an overload. Of course, the overload detector may be adjusted for a desired maximum load but it would usually be left in one position. It will be noted that the switch element 36 operates with the switch element 30 so that no matter which transducer is selected for reading by the switch element 30, the switch element 36 will feed the total load on the press as read by the ram transducer to the overload detector.

It will be understood that invention is not being claimed in any of the individual elements shown in FIG. 5 other than the transducers. All of these elements are available commercially on the open market.

It will be understood that in its simplest embodiment, the present invention would involve a single transducer on the ram whereby the total load on the press is read. The high and low density limits would therefore apply only to the overall reading of the ram transducer. Similarly, going in the other direction, if expense is no objection, a meter may be provided for each of the transducers so that the switch element could be eliminated and readings could be obtained at any time from any of the transducers.

With regard to the density control system, it will be understood that the upper and lower set points may be adjusted independently anywhere within the range of the indicating meter. In other words, they may be set far apart or extremely close together, as may be appropriate. The Cal. limits position of the switch element 31 makes it possible to preset these set points to any point within the range of the indicating meter without putting a load on the machine after the machine has initially been calibrated. It is possible to obtain a set point accuracy of plus or minus one-half percent of full tonnage at any point within the indicating range of the instrument.

In starting up an operation according to the present invention, the switch element 31 is placed in the zero position. In this position the amplifier is automatically balanced to zero. The element 31 is then moved to the meter calibration position at which point the meter is automatically calibrated. The element 31 is then moved to the Cal. limits position at which the high and low limit settings are manually calibrated. When calibration is complete, the element 31 is set for either low or high scale operation and then during operation of the machine, the operator may periodically move the switch element 30 to check the readings from the various transducers. Thus, for example, if pieces are being rejected because of too high or too low a density, the opera-tor can check each of the transducers and find out which one is contributing to the defective reading. If, for example, the standard platen is giving too high or too low a reading, that particular platen can then be adjusted as described in the said Belden patent until it gives a reading within the required limits. If the relation between the readings of the several transducers is apparently correct but the total reading from the ram transducer is too high or too low, it is an indication that something is wrong with the powder mix.

It will also be understood that the arrangement herein disclosed may be elaborated as much as desired and as the economics of the situation warrants, as, for example, by having automatic means for adjusting the several platens through the high and low limit relay device based on incorrect readings from the respective platen transducers.

By way of example as to what may be accomplished by the high and low limit relays, a gating arrangement is shown in FIGS. 7 and S. In these figures, D represents the top platen which carries the outer die and carries noload. By reference to the aforesaid Belden patent, it will be noted that when a completed workpiece is ejected it comes out on the top of the platen D in a position shown n broken lines in FIG. 7 at 40. As further described in said Belden patent, the workpiece is then pushed aside before the next powder filling operation begins.

In FIG. 7 there is indicated a gate member 41 having three channels 42, 43, and 44. The gate member is pivoted on the platen D at the point P. The channels 42, 43 and 44 lead to a chute member where the paths flare outwardly as at 42a, 43a, and 440. A small air cylinder 45 is mounted on a top plate 46 of the gate 41 and the piston rod 47 of the air cylinder is connected to a lug 48 secured to the pivoted gate. The piston in the cylinder 45 is supplied with air through the pipes 49 and 50 from a source 51 through a valve 52 actuated by solenoids 53 and 54. In its normal position, the gate will be pivoted clockwise as seen in FIG. 7 so that workpieces completed and ejected will enter the channel 42 and the chute 42a, and the gate will remain in this position so long as the minimum density is not being attained. If the minimum allowable density is attained, the appropriate solenoid actuates the valve 52 to shift the gate to the position shown in FIG. 7 and as long as the minimum density is being attained, the workpieces will pass through the channels 43 and 43a. If an excessive density is achieved, the

relays function to actuate the valve to swing the gate counterclockwise to the point where the workpieces will be kicked into the channels 44 and 4441. In this way workpieces within limits may be collected in one bin, whereas low density pieces may be collected in another bin and high density pieces in a third bin.

Numerous modifications may be made without departing from the spirit of the invention and no limitation is therefore intended which is not specifically set forth in the claims which follow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a multi-platen compacting press having a ram, a fixed die platen, and a plurality of load bearing floating die platens, means to measure the density being produced in the compacted workpiece in the annular portions thereof between the ram and each of said dies, comprising a transducer associated with said ram and a transducer associated with each of said load bearing die platens to sense the pressure exerted thereby, and means for indicating the pressure sensed by each of said transducers.

2. A multi-platen compacting press according to claim 1, wherein each of said transducers comprises an annular element on said ram and on each said die platen, said ram annular element being subjected to the total compressive force of the press, and said die platen annular elements being subjected respectively to the compressive forces exerted on the several platens, and a strain gauge secured to each of said annular elements.

3. A multi-platen compacting press according to claim 2, wherein each of said annular elements; has four strain gauges secured thereto in diametrically opposed pairs, one pair being disposed to sense axial shortening of the annular element due to compression thereof, and the other pair being disposed to sense increase in circumference of the annular element due to compression thereof.

4. A multi-platen compacting press according to claim 3, wherein said four strain gauges in opposed pairs are electrically connected in a Wheatstone bridge arrangement, D.C. means for energizing said bridge across two opposed terminals thereof, and means for indicating a change of potential across the other opposed terminals thereof.

5. A multi-platen compacting press according to claim 4, wherein means are provided to amplify the said change of potential, said means being connected to a meter to indicate said amplified change of potential.

6. A multi-platen compacting press according to claim '5, wherein a peak motion indicator is operatively associated with said meter so that the very brief signal from said bridge is held sufficiently long to be readable by the human eye.

7. A multi-platen compacting press according to claim 1, wherein each of said transducers produces an electrical signal, and a single indicating means is provided to indicate such signal, and electrical switching means are provided to connect the signal from any one of said transducers to said indicating means.

8. A multi-platen compacting press according to claim 1, including means to establish a minimum and a maximum allowable density indication, and means operative upon the occurrence of a density indication beyond said minimum or maximum, to signal such occurrence.

9. A multi-platen compacting press according to claim 8, wherein said press includes means to discharge a compacted workpiece, and means directing said discharged workpiece into one path when its density is within the established limits, and into another path when its density is beyond said minimum or maximum.

10. A multi-platen compacting press according to claim 9, wherein separate paths are provided for workpieces whose density is below said minimum and for workpieces whose density is above said maximum, and said directing means is arranged to direct the sub-minimum and 10 supra-maximum workpieces into the last mentioned paths respectively.

References Cited UNITED STATES PATENTS 2,448,277 8/1948 Renier 18-16 2,561,266 7/1951 Dietert 18-16 2,883,703 4/1959 Frank 18-16.7

I. HOWARD FLINT, JR., Primary Examiner. 

1. IN A MULTI-PLATEN COMPACTING PRESS HAVING A RAM, A FIXED DIE PLATEN, AND A PLURALITY OF LOAD BEARING FLOATING DIE PLATENS, MEANS TO MEASURE THE DENSITY BEING PRODUCED IN THE COMPACTED WORKPIECE IN THE ANNULAR PORTIONS THEREOF BETWEEN THE RAM AND EACH OF SAID DIES, COMPRISING A TRANSDUCER ASSOCIATED WITH SAID RAM AND A TRANSDUCER ASSOCIATED WITH EACH OF SAID LOAD BEARING DIE PLATENS TO SENSE THE PRESSURE EXERTED THEREBY, AND MEANS FOR INDICATING THE PRESSURE SENSED BY EACH OF SAID TRANSDUCERS. 